EP 0 593 517 B1 discloses an electromagnet system of the species initially cited wherein the core has its cylindrical shaft plugged through a round hole of the yoke leg proceeding from the outside and has the core section of its end side clamped in a bore of the yoke leg. For clamping and for setting the final position, the core is thereby charged with pulse-like impacts. Although a good interference seat of the core derives in this way, the pulse-like impacts can produce undesired jolts and friction at other elements connected to the magnet system, for example at contacts. Moreover, the adjustment of the core therein is possible only in one direction, namely in the direction of the core insertion.
DE 31 48 052 A1 also already discloses an electromagnetic relay whose coil core is secured with a fine thread in a bore likewise correspondingly provided with a fine thread, being secured and adjusted by being screwed in. This exact screw connection, however, not only requires complicated manufacture and assembly of the parts but it by itself also does not produce an adequate interference fit, so that additional fixing means are required. For example, it is thus proposed to apply a plastic adhesive onto the fine thread or to provide the core with an additional counternut for securing. This requires an additional outlay; further, the fixing agent in the thread can deteriorate the magnetic coupling, whereas the additional counter-nut also requires additional space.
An object of the invention is to improve an electromagnet system of the species initially cited such that a good and dependable connection and magnetic coupling of core and yoke is achieved in a simple way, whereby this connection should be capable of being exactly adjusted - namely both forward as well as backward.
This object is inventively achieved in that a thread is fashioned on the conical section of the core, said thread being turned self-deforming into the inherently thread-free wall of the likewise conically expanded recess of the yoke.
Given the inventive magnetic system, thus, the conical section of the core and the conical inside wall of the round hole in the yoke section are already matched to one another. The ultimate fastening in one another and the fine positioning, however, ensue by turning via the thread fashioned on the cone section of the core, this digging into the smooth inside surface of the round hole when turned in. It is comparatively simple to manufacture this one thread on the core since a mating with a correspondingly pre-fabricated, complementary nut thread in the yoke is not required. Due to the displacement of the material when the thread core is screwed into the yoke section, an excellent interference seat as well as a good magnetic coupling between these two parts derive without auxiliary measures. An especially good coupling derives when the thread on the core is fashioned as flat thread, (i.e. when the individual turns of the thread channel or, respectively, of the thread channels given multiple-start threads) exhibit a large spacing in relationship to the channel depth, so that a flattened thread web arises that is trapezoidal in cross section or approximately saw-tooth-shaped given a sidewall that is steeper at one side.
The cone section of the core and the conical inside wall of the round hole in the yoke can, for example, have an angle between 0.5 .degree.and 5.degree. relative to the core axis. However, an angle similar to conical sleeves and conical shafts for self-locking tool fastening is preferably selected. The angle of the cone envelope relative to the axis thereby lies between 1.degree. and 2.degree., preferably at approximately 1.5.degree. (1.degree. 30 minutes) or, respectively, between 1.degree. 25 minutes and 1.degree. 30 minutes in what is referred to as a Morse cone. Given this slight slope angle, it would also be conceivable to fashion that shaft of the core with the fastening section continuously slightly conically (with approximately 1.degree. slope). The thread can be especially simply produced on the cone section when the thread channel or, respectively, thread channels exhibits (or, respectively, exhibit) a constant inside core diameter. This means that the thread has not been or has only been slightly dug in at the narrowest location of the cone section wherein it is cut in deeper and deeper toward the broadened end. An especially simple manufacture and processing derives given fashioning as rolling thread.
For improving the magnetic properties, both the yoke as well as the core are expediently soft-annealed. The soft-annealed yoke also has the advantage that it easily widens or, respectively, deforms when the threaded core is turned in, that excessively high torques are not required. It is advantageous at the core when it is annealed before the thread is rolled on, since the warp at the thread walls produced by material displacement when rolling the thread experiences a certain hardening and thus digs more easily into the soft-annealed, thread-free material of the round hole when the core is turned in.
Moreover, a surface coating of copper or copper-graphite can facilitate the turning and prevent ceasing. This can ensue nearly without additional outlay since a coating, for example with Cu, is desirable anyway as corrosion protection. The thread proceeds partly only in the coating, which serves as a type of lubrication.
An inventive method for joining core and yoke in the inventive electromagnet system comprises essentially the following steps:
producing a conical round hole in the yoke section; PA1 producing a core with a cylindrical shaft and a cone section at one end of the core that expands toward the free end; PA1 producing a thread on the cone section; PA1 plugging the cylindrical shaft of the core through the round hole of the yoke section until the cone section clamps in the round hole; and PA1 turning the core in thread direction upon application of an axial force until the free end of the cylindrical shaft has reached a predetermined position.
In an embodiment, the present invention provides an electromagnet system comprising a yoke comprising a transverse section having a round hole; and a core comprising a fastening end secured in a the round hole the transverse section of the yoke, the core further comprising a cylindrical shaft connected to a conical section which is connected to the fastening end of the core, at least a portion of the conical section being larger in diameter than the round hole, the conical section further comprising a threaded section that extends to the fastening end, the threaded section of the conical section of the core engaging the round hole of the transverse section of the yoke.
In an embodiment, the conical section of the core expands conically in diameter as the conical section extends from the cylindrical shaft towards the fastening end.
In an embodiment, the threaded section on the conical section of the core comprises a flattened thread web.
In an embodiment, the thread web comprises a trapezoidal cross section.
In an embodiment, the thread web comprises a saw tooth-shaped cross section.
In an embodiment, the conical section of the core has an outer surface and a central axis and a slope angle of its outer surface relative to its central axis ranging from 0.5.degree. to 5.degree..
In an embodiment, the slope angle ranges from 1.degree. to 2.degree.
In an embodiment, the slope angle is about 1.5.degree..
In an embodiment, the threaded section comprises a thread channel, the thread channel having a constant diameter throughout the threaded section.
In an embodiment, the threaded section comprises a rolled thread.
In an embodiment, the yoke and the core are soft-annealed.
In an embodiment, the fastening end comprises an axial prismatic recess for receiving a rotating tool.
In an embodiment, the present invention provides a method for joining a core and a yoke in an electromagnet system, the method comprising the following steps: providing a yoke; producing a conical round hole in the yoke; manufacturing a core with a cylindrical shaft connected to a conical section that expands in diameter as it extends from the cylindrical shaft towards a fastening end of the core, the cylindrical shaft comprising a free end; producing a thread on the conical section; inserting the cylindrical shaft of the core through the round hole of the yoke section until the conical section engages the round hole; and rotating the core while applying an axial force towards the round hole until a free end of the cylindrical shaft has reached a predetermined position.
In an embodiment, the step of producing the conical round hole comprises punching the hole through the yoke with a conical pin.
In an embodiment, the step of producing the thread comprises using a rolling process.
In an embodiment, the step of producing the conical round hole in the yoke comprises soft-annealing the yoke after the production of the conical round hole.
In an embodiment, the step of producing the core comprises soft-annealing the core before the step of producing the thread on the conical section of the core.
Other objects and advantages of the present invention will become apparent from reading the following detailed description and appended claims, and upon reference to the accompanying drawings.